[MODULARIZE=instance] Enable direct running of output under v8 (#24337)

Author: sbc100

.circleci/config.yml

@@ -649,6 +649,7 @@ jobs:
             wasmfs.test_fs_llseek_rawfs
             wasmfs.test_freetype
             minimal0.test_utf
+            instance.test_async_hello_v8
             "
   test-wasm2js1:
     environment:

src/postamble.js

@@ -341,6 +341,13 @@ if (ENVIRONMENT_IS_NODE
 }
 #endif
 
+#if ENVIRONMENT_MAY_BE_SHELL
+if (ENVIRONMENT_IS_SHELL) {
+  // When run in a shell we run `init` immediately.
+  await init();
+}
+#endif
+
 #else
 preInit();
 run();